Implement ScriptPromise and ScriptFunction

Source/bindings/v8/ScriptPromise.h

+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
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+ * modification, are permitted provided that the following conditions are
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+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef ScriptPromise_h
+#define ScriptPromise_h
+
+#include "ScopedPersistent.h"
+#include "ScriptFunction.h"
+#include "V8ScriptRunner.h"
+
+#include <v8.h>
+
+namespace WebCore {
+
+// ScriptPromise is a class for hooking into the then() chain for a
+// Promise from the C++ world.
+//
+// To use this, provide a subclass of ScriptFunction where the 'call'
+// method the function to pass to 'Promise.then'.
+//
+// class MyCallback : public ScriptFunction {
+// public:
+//   MyCallback(PassRefPtr<MyClass> reciever) : m_receiver(receiver) { }
+//   virtual void call(ScriptValue scriptValue) {
+//     m_receiver->HaveValue(scriptValue.v8Value().As<v8::Integer>()->Value())
+//     m_value =

[abarth-chromium, 2013/08/09 21:46:52]

This code same seems incomplete...

+//   }
+//   int value() const { return m_value; }
+//
+// private:
+//   RefPtr<MyClass> m_receiver;
+// };
+//
+// void MyClass::saveValue(ScriptPromise* promise) {
+//   m_resultCallback = adoptRef(new MyCallback(this));

[abarth-chromium, 2013/08/09 21:46:52]

Doesn't this example code create a reference cycle?  MyClass holds a RefPtr to
MyCallback, which holds a RefPtr to MyClass...  You don't need to hold a RefPtr
to ScriptFunction in MyClass.  The lifetime of the ScriptFunction will be
managed by the GC.

+//   promise->then(m_resultCallback);
+// }
+//
+// void MyClass::HaveValue(int value) {
+//   .. deal with the value here.
+// }
+class ScriptPromise {
+public:
+    ScriptPromise() : m_isolate(0) { }

[abarth-chromium, 2013/08/09 21:46:52]

Can we remove this constructor?  ScriptPromise should be a short-lived object
that you only construct when you have a v8::Handle<v8::Value> that you want to
interact with.

+    explicit ScriptPromise(v8::Handle<v8::Value> promise, v8::Isolate* isolate)

[abarth-chromium, 2013/08/09 21:46:52]

I would have expected this object to take a ScriptValue rather than a
v8::Handle<v8::Value>.  The code using this class is going to be outside the
bindings directory, so it's likely to be dealing in ScriptValue rather than in
the lower-level V8 handles.

+        : m_promise(promise)
+        , m_isolate(isolate) { }
+
+    void Reset(v8::Handle<v8::Value> promise, v8::Isolate* isolate)
+    {
+        m_promise.set(isolate, promise);
+        m_isolate = isolate;
+    }

[abarth-chromium, 2013/08/09 21:46:52]

I'd skip this function.

+
+    void clear()
+    {
+        m_isolate = 0;
+        m_promise.clear();
+    }

[abarth-chromium, 2013/08/09 21:46:52]

This one too.

+    bool then(ScriptFunction* function, ScriptExecutionContext* context) const

[abarth-chromium, 2013/08/09 21:46:52]

I'd probably take a PassRefPtr<ScriptFunction> function because most callers
will want to give us their last reference.

There's no need for the |ScriptExecutionContext| parameter.  We should get that
from the static via getScriptExecutionContext().  If we let the caller supply a
|ScriptExecutionContext|, they could give us the wrong one.

+    {
+        v8::Handle<v8::Value> promise = m_promise.newLocal(m_isolate);
+        if (!promise->IsObject()) {
+            return false;
+        }

[abarth-chromium, 2013/08/09 21:46:52]

No need for { }.

Also, don't we need to check promise.IsEmpty() before using operator->  ?

+        v8::Handle<v8::Object> promiseObject = promise.As<v8::Object>();
+        v8::Handle<v8::Value> then = promiseObject->Get(v8::String::NewSymbol("then"));
+        if (then.IsEmpty() || !then->IsFunction())
+            return false;
+
+        v8::Handle<v8::Value> argv[] = {
+            function->toV8(m_isolate)
+        };
+        V8ScriptRunner::callFunction(then.As<v8::Function>(), context, promiseObject, WTF_ARRAY_LENGTH(argv), argv);
+        return true;
+    }
+
+private:
+    ScopedPersistent<v8::Value> m_promise;
+    v8::Isolate* m_isolate;
+};
+
+} // namespace WebCore
+
+
+#endif // ScriptPromiseResolver_h